This invention relates to an apparatus for forming, stamping and stacking (discharging) articles made of a thermoplastic sheet material, wherein all three operational steps are performed in a single station, hereafter referred to as the forming station. Prior to its admission to the forming station, the thermoplastic sheet is heated and then it is intermittently advanced into the forming station. A forming tool secured to a height-adjustable platform is arranged in the forming station. Above the forming tool there is arranged a stacking shaft into which the formed articles are admitted subsequent to their separation from the sheet.
An apparatus of the above-outlined type is disclosed in German Laid-Open Application (Offenlegungsschrift) No. 2,517,981. The apparatus described therein shapes the articles by pressurized air and provides for an intermittent displacement of the stacking shafts and the pressure hood. Such an apparatus is structurally complex and expensive since relatively large masses have to be moved with high frequency (approximately forty times per minute). For this reason it has already been proposed to arrange the stacking shafts stationarily and to introduce a slide intermittently between the stacking shafts and the molds. In this manner a closed space (chamber) is formed which communicates with the other tool parts into which the pressurized article-forming air may be introduced.
In the above-outlined arrangement, however, difficulties have been encountered to effect a seal around the slide for keeping the pressurized air within the chamber closed by the slide. To improve such a seal, it has been attempted to use a rubber-coated slide. Wear, however, occured rapidly, resulting in a deterioration of the sealing properties.